Problem with css in web kit

I just did some mods to a theme for a client and they are reporting some funny issues with their webkits browsers. I've checked on Chrome and Safari and everything looks good for me, not sure why they are having issues though.

The URL is american mug and stein (all one word .com)they claim when they click the button it loads a box underneath the button before transfering them on.

Full disclosure: The button is an affiliate link. If you dont want to click it don't, or if you want to help test their claim out do, then clear your cookies if you're affraid of getting tracked/whatever.